1. Field of the Invention
The present invention relates to temperature gauges for ceramic susceptors that are installed in semiconductor manufacturing equipment, and to ceramic susceptors, as well as semiconductor manufacturing equipment, utilizing the temperature gauges.
2. Description of the Background Art
Ceramic susceptors (also called wafer holders) formed from an inorganic insulating material such as a ceramic of high thermal conductivity, and in which a resistive heating element is embedded, have been employed to date in semiconductor manufacturing equipment such as CVD devices and plasma CVD devices, for example, for uniformly heating wafers on which film-forming or like processes are carried out.
In order to control the heating temperature by varying the amount of voltage and current applied to the resistive heating element, a plurality of terminals connected to the resistive heating element is furnished exposed on a face of the susceptor apart from its wafer-heating face, and the terminals and an external power source are connected by lead lines. Likewise, in order to control the temperature of the ceramic susceptor itself, a thermoelectrically matched temperature measuring component is furnished exposed on a face apart from the wafer-heating face.
With the enlarging in diametric span of wafers lately, severe demands are being placed on the temperature-control regimen for the wafer-heating face of ceramic susceptors in order to improve product yields in semiconductor manufacturing equipment. Consequently, uniformly and precisely controlling the temperature of the wafer-heating face is necessary, and temperature-measuring accuracy in the temperature-measuring components that control the output from the resistive heating element has become crucial.
Nevertheless, in measuring temperature within the reaction chambers in semiconductor manufacturing equipment, accurate temperature measurement has been difficult because the behavior of gas molecules in the temperature-measuring component environs is altered on account of pressure fluctuations stemming from the introduction and discharge of reaction gases, drastically changing how the molecules move thermally. Moreover, in cases in which the location where the temperature-measuring components are installed is remote from the wafer-heating face, the measurement temperature departing from the actual wafer temperature leads to a pronounced temperature gradient, which consequently has, depending on the case, invited circumstances in which the wafer is damaged by thermal stress.
In Japanese Pat. Pub. No. 2,644,660, for example, this is dealt with by providing a sheath in which a thermocouple is fixed and male threads on the tip portion of the sheath, which is made of metal, and by providing female threads in the ceramic susceptor, in a face of apart from its wafer-heating face, or in matter consisting of metal, ceramic, etc. embedded therein, with the male threads furnished on the tip portion for the thermocouple being screwed together with and fixed into the female threads. This enlarges the surface area in which the thermocouple and the ceramic susceptor are in direct contact, and at the same time because they are fixed by being screwed together their state of contact is unlikely to change, whereby the temperature measuring accuracy can be improved. Furthermore, the thermocouple itself is detachable/replaceable.
In other ceramic susceptor examples, proposed in Japanese Pat. App. Pub. No. 2001-244049, Japanese Pat. App. Pub. No. 2001-85143, and Japanese Pat. App. Pub. No. 2001-85144, departure between measurement temperature and wafer temperature is prevented by establishing bottomed holes, directed from the side opposite the wafer-heating face to the heating face and into which a thermocouple is inserted, and making the bottoms of the bottomed holes relatively nearer the wafer-heating face than the heating element. In addition the thermocouples are resin-sealed inside the bottomed holes after being joined into them with a brazing material, or are fixed inside the bottomed holes by filling them in with an insulating material such as a heat-resistant resin or a ceramic.
In a further ceramic susceptor example, Japanese Pat. App. Pub. No. 2002-164291, a recess whose aperture surface area is 1.0 to 30 mm2, whose depth d is, with respect to the thickness t of the heater, t/4≦d≦3t/4 is formed in the face on the side opposite the surface-heating side, and a thermocouple whose filament diameter is 0.05 to 1.0 mm and the tip portion of which is equipped with a temperature-gauging contact is inserted and adhesively fixed by means of a filler into the recess. That the temperature-measuring responsiveness is thereby improved, reducing transient temperature irregularities when heating a wafer and shortening the time until the temperature stabilizes is therein proposed.
A drawback with the ceramic susceptors set forth in the publications discussed above has been that with heat from the temperature-gauging site on the ceramic susceptor not being readily transmitted to the temperature-gauging contact, owing to the presence, surrounding the temperature-gauging contact that is on the tip of the thermocouple, of the sheath, the embedded matter consisting of metal or ceramic, or the insulating material or filler material consisting of a heat-resistant resin or ceramic, it takes time for the measurement temperature to stabilize.
Another problem has been that the temperature-measuring element generally employed in thermocouples is thin-gauge because it must be confined within limited space, and consequently the temperature-measuring element, undergoing impact on the device itself or thermal shock when wafers are heated, is in some cases damaged. With the ceramic susceptors set forth in the disclosures in Japanese Pat. App. Pub. No. 2001-244049, Pat. App. Pub. No. 2001-85143, Pat. App. Pub. No. 2001-85144, and Pat. App. Pub. No. 2002-164291, in particular, because the temperature-measuring element is fixed by being joined or embedded in place, replacing the entire ceramic susceptor is necessary if the temperature-measuring element has been damaged, which has made the replacement work a large-scale undertaking, and on top of that the costs attendant on replacement have been great.